Complete overhaul of the campaign system, so that alien activity changes depending on the player's actions
New capabilities for the rendering engine, including bumpmapping, specular lighting, glowmapping, flare support, texture blending and more
A new tactical overhead map
Alien bases have been added and the player can mount an assault on them
Support for crashed UFO missions
Overhauls of the map editor
Loads of new maps and new tiles for existing maps that are randomly generated
New weapons
New music and sound effects
And loads of behind-the-scenes optimizations and tweaks for everything from the pathfinding to the user interface